This invention relates to electrostatic spray guns for spraying paint and the like, and more specifically relates to an electrostatic spray gun voltage monitoring system wherein the operating voltage of the spray gun may be monitored at a location remote from the spray gun.
In the operation and use of electrostratic spray guns there is a need to be aware of the operating electrostatic voltage of the spray gun during use, and there is also a need to know the magnitude of the electrostatic current delivered by the spray gun during use. The electrostatic voltage is important in terms of controlling efficiency of the painting operation, for the ability of the spray gun to efficiently deliver paint to the article is directly related to the spray gun voltage. As the voltage decreases the spray painting efficiency also decreases, and a larger volume of paint spray particles are not attracted to the article, but rather pass the article as overspray, and this overspray contributes to environmental pollution. Special spray booth constructions must be prepared in order to collect and dispose of overspray, adding to the cost of the overall painting system. It is important to monitor the magnitude of the spray gun current, for higher current levels indicate the possibility of an imminent hazardous ignition condition. Since it is known that electrostatic spray guns are operated in an environment containing highly volatile or flammable materials, the possibility of explosions must always be kept in mind and the need to monitor current is therefore very important.
Further, the hazardous environment of spray gun operation dictates that electrical connections to an electrostatic spray gun be held to a minimum, and where necessary, be maintained in an extremely secure explosion-proof and intrinsically safe environment. It is preferable to operate electrostatic spray guns without any electrical connections whatsoever to external circuitry or power sources, so that no possibility exists of electrical shorting to the external environment. The assignee of the present invention has developed a line of electrostatic spray guns which are operated solely by high-pressure air transmitted to the gun, and wherein the air is used not only for spraying the paint but also to drive a self-contained turbine generator within the electrostatic spray gun body. The output of the turbine generator is used to develop a suitable high voltage which is applied to an electrode in the electrostatic spray gun, to develop the necessary electrostatic field for efficient painting operations. Because this spray gun operates with no external electrical connections it is a particular problem to monitor the voltage and current generated at the spray gun, especially when there is a need to monitor such voltage and current at a remote location.
Several prior patents disclose features which are related to some of the features of the present invention, the disclosures of which are incorporated by reference herein. U.S. Pat. No. 4,219,865, issued Aug. 26, 1980, discloses an energy converting an electric power generating system for electrostatic spray guns, wherein the kinetic energy available in a moving air stream is converted into electrical power by means of an air turbine/alternator/high voltage power supply. U.S. Pat. No. 4,290,091, issued Sep. 15, 1981, discloses some of the circuit features which are usable with the air turbine power supply in an electrostatic spray gun. U.S. Pat. No. 4,462,061, discloses certain improvements in the air passages in an air turbine electrostatic spray gun. U.S. patent application Ser. No. 478,276, filed Feb. 9, 1990, discloses an electrostatic spray gun of the foregoing type, having a remote voltage and current monitor circuit utilizing fiber-optic cables for signal transmission. All of the foregoing patents are owned by the assignee of the present invention.